Neurons, Hormones, and the Brain

The Nervous System

The nervous system is a complex, highly coordinated network of tissues that communicate via electro chemical signals. It is responsible for receiving and processing information in the body and is divided into two main branches: the central nervous system and the peripheral nervous system.

The Central Nervous System

The central nervous system receives and processes information from the senses. The brain and the spinal cord make up the central nervous system. Both organs lie in a fluid called the cerebrospinal fluid, which cushions and nourishes the brain. The blood-brain barrier protects the cerebrospinal fluid by blocking many drugs and toxins. This barrier is a membrane that lets some substances from the blood into the brain but keeps out others.

The spinal cord connects the brain to the rest of the body. It runs from the brain down to the small of the back and is responsible for spinal reflexes, which are automatic behaviors that require no input from the brain. The spinal cord also sends messages from the brain to the other parts of the body and from those parts back to the brain.

The brain is the main organ in the nervous system. It integrates information from the senses and coordinates the body’s activities. It allows people to remember their childhoods, plan the future, create term papers and works of art, talk to friends, and have bizarre dreams. Different parts of the brain do different things.

The Peripheral Nervous System

All the parts of the nervous system except the brain and the spinal cord belong to the peripheral nervous system. The peripheral nervous system has two parts: the somatic nervous system and the autonomic nervous system.

The Somatic Nervous System

The somatic nervous system consists of nerves that connect the central nervous system to voluntary skeletal muscles and sense organs. Voluntary skeletal muscles are muscles that help us to move around. There are two types of nerves in the somatic nervous system:

• Afferent nerves carry information from the muscles and sense organs to the central nervous system.
• Efferent nerves carry information from the central nervous system to the muscles and sense organs.

The Autonomic Nervous System

The autonomic nervous system consists of nerves that connect the central nervous system to the heart, blood vessels, glands, and smooth muscles. Smooth muscles are involuntary muscles that help organs such as the stomach and bladder carry out their functions. The autonomic nervous system controls all the automatic functions in the body, including breathing, digestion, sweating, and heartbeat. The autonomic nervous system is divided into the sympathetic and parasympathetic nervous systems.

• The sympathetic nervous system gets the body ready for emergency action. It is involved in the fight-or-flight response, which is the sudden reaction to stressful or threatening situations. The sympathetic nervous system prepares the body to meet a challenge. It slows down digestive processes, draws blood away from the skin to the skeletal muscles, and activates the release of hormones so the body can act quickly.
• The parasympathetic nervous system becomes active during states of relaxation. It helps the body to conserve and store energy. It slows heartbeat, decreases blood pressure, and promotes the digestive process.